Reoviridae viruses, which have a genome consisting of double stranded RNA (dsRNA), cause many diseases. Orbiviruses which are viruses of the Reoviridae family, also cause widespread disease. Examples of Orbiviruses are African Horse Sickness Virus (AHSV), Epizootic Hemorrhagic Disease Virus (EHDV) and Bluetongue virus (BTV).
African Horse Sickness Virus (AHSV), Epizootic Hemorrhagic Disease Virus (EHDV) and Bluetongue virus (BTV) are non-contagious, viral diseases of ruminants and are commonly spread by insect vectors. AHSV commonly affects horses, mules, donkeys and zebras; EHDV commonly affects deer, cattle and sheep; and BTV commonly affects cattle, sheep, goats, buffalo, deer, dromedaries and antelope.
Bluetongue virus (BTV) is an insect-vectored emerging pathogen of wild ruminants and livestock which has had a severe economic impact on European agriculture. BTV causes disease in sheep, goats, and cattle with mortality reaching 70% in some breeds of sheep. BTV is transmitted between mammalian hosts by several species of biting midges in the Culicoides genus, which determine its geographic range. BTV is endemic in many tropical and sub-tropical countries, but since 1998 incursions of BTV into mainland Europe have been common events, reaching as far north as the UK in 2007. Molecular epidemiology studies show that six different serotypes (BTV1, 2, 4, 8, 9, and 16) have been introduced into mainland Europe since 1998, on at least eight separate occasions, via at least three different routes, involving new introductions in most years since 1998. The probable direct causes for the increased range of BTV are the increased distribution and size of insect vector populations, and the transmission of BTV by novel vector species, which are abundant in central and northern Europe. The existence of undiagnosed infections of livestock or wild ruminants coupled with the rapid spread over large distances through movement of the insect vector has resulted in a failure to prevent BTV becoming endemic in Europe. Thus, BTV now represents a considerable threat to livestock in all European countries. Four BTV serotypes are now common in Europe and have resulted in the deaths of 1.8 million animals.
The control of BTV through vaccination has been attempted in Europe using both live and inactivated vaccines to a small number of serotypes. Both types of vaccine have provided some protection for regions in Europe, but have known drawbacks. Live attenuated BTV vaccines suffer from a number of drawbacks: 1) under-attenuation leading to the development of typical bluetongue clinical symptoms; 2) reversion to virulence or re-assortment with wild-type virus followed by spread via the insect vector; 3) inability to distinguish vaccinated animals from naturally infected animals precluding the use of a differentiation of infected from vaccinated animals (DIVA) strategy; and 4) time delay to produce attenuated strains of newly circulating serotypes.
Inactivated vaccines have been used to control BTV2 and BTV4 in Europe. These suffer from the high production costs associated with inactivation, confirming the inactivation of every batch, and low immunogenicity.
It has previously been reported by the inventors that BTV ssRNA is infectious without the use of a helper virus and infectious BTV can be recovered from cells (Boyce, M. and Roy, P. 2007). This document is incorporated herein in its entirety.